Platelet activating factor (PAF, 1-o-alkyl-2-acetyl-sn-glycerol-3-phosphorylcholine) is a potent inflammatory phospholipid mediator with a wide variety of biological activities. PAF was initially identified as a water soluble compound released by immunoglobulin E (IgE)-sensitized rabbit basophils. It is now known that PAF is also generated and released by monocytes, macrophages, polymorphonuclear leukocytes (PMNs), eosinophils, neutrophils, natural killer lymphocytes, platelets and endothelial cells, as well as by renal and cardiac tissues under appropriate immunological and non-immunological stimulation. (Hwang, "Specific receptors of platelet-activating factor, receptor heterogeneity, and signal transduction mechanisms", Journal of Lipid Mediators 2, 123 (1990)). PAF causes the aggregation and degranulation of platelets at very low concentrations. The potency (active at 10.sup.-12 to 10.sup.-9 M), tissue level (picomoles) and short plasma half life (2-4 minutes) of PAF are similar to those of other lipid mediators such as thromboxane A, prostaglandins, and leukotrienes.
PAF mediates biological responses by binding to specific PAF receptors found in a wide variety of cells and tissues. Structure-activity studies on PAF and its analogs indicate that the ability of PAF to bind to these receptors is structure specific and stereospecific. (Shen, et al., "The Chemical and Biological Properties of PAF Agonists, Antagonists, and Biosynthetic Inhibitors", Platelet-Activating Factor and Related Lipid Mediators, F. Snyder, Ed. Plenum Press, New York, N.Y. 153 (1987)).
While PAF mediates essential biological responses, it also appears to play a role in pathological immune and inflammatory responses. Many published studies have provided evidence for the involvement of PAF in human diseases, including arthritis, acute inflammation, asthma, endotoxic shock, pain, psoriasis, ophthalmic inflammation, ischemia, gastrointestinal ulceration, myocardial infarction, inflammatory bowel diseases, and acute respiratory distress syndrome. Animal models also demonstrate that PAF is produced or increased in certain pathological states.
The involvement of PAF in pathological inflammatory and immune states has stimulated a substantial research effort to identify PAF receptor antagonists. In 1983, a phospholipid analog referred to as CV-3988 (rac-3-(N-n-octadecyl-carbamoyloxy-.omega.-methoxypropyl-2-thiazolioethyl phosphate) was reported to have PAF receptor antagonist properties. (Terashita, et al., Life Sciences 32, 1975 (1983).) In other early work in this area, Shen, et al., (in Proc. Natl. Acad. Sci. (U.S.A.) 82, 672 (1985)), reported that kadsurenone, a neolignan derivative isolated from Piper futokadsura Sieb et Zucc (a Chinese herbal plant) was a potent, specific and competitive inhibitor of PAF activity at the receptor level.
Hwang, et al., disclosed in 1985 that trans-2,5-bis-(3,4,5-trimethoxyphenyl) tetrahydrofuran (L-652,731) inhibits the l- binding of tritiated PAF to PAF receptor sites. (Hwang, et al., "Trans-2, 5-bis-(3,4,5-trimethoxyphenyl)tetrahydrofuran", Journal of Biological Chemistry 260, 15639 (1985).) L-652,731 was found to be orally active, and to inhibit PAF-induced rat cutaneous vascular permeability at a dosage of 30 aglkg body weight. The compound was found to have no effect on the enzyme 5-lipoxygenase. Hwang, et al. also reported that trans-L-652,731 (wherein the aryl groups at the 2 and 5 positions are on opposite sides of the plane of the tetrahydrofuran ring) is approximately 1000 times more potent than cis-L-652,731 (wherein the 2 and 5 aryl substituents are on the same side of the plane of the tetrahydrofuran ring).
In 1988, Hwang, et al., reported that L-659,989 (trans-2-(3-methoxy-4-propoxyphenyl-5-methylsulfonyl)-5-(3,4,5-trimethoxyp henyl)tetrahydrofuran) is an orally active, potent, competitive PAF receptor antagonist, with an equilibrium inhibition constant 10 times greater than that of trans-L-652,731. (Hwang, et al., J. Pharmacol. Ther. 246, 534 (1988).)
U.S. Pat. Nos. 4,996,203, 5,001,123 and 4,539,332 to Biftu, et al. and European Patent Application Nos. 89202593.3, 90306235.4, and 90306234.7 disclose that specific classes of 2,5-diaryl tetrahydrofurans are PAF receptor antagonists.
Bowles et al., Synlett, 1993, pp 111 disclose a limited number of substituted tetrahydrofurans which may possess PAF receptor antagonism.
Danyoshi et al., Chem. Pharm. Bull., 1989, pp 1969, disclose 2-substituted-N-alkoxycarbonyl pyrrolidines which inhibit PAF induced rabbit platelet aggregation.
Leukotrienes, like PAF, are potent local mediators, playing a major role in inflammatory and allergic responses, including arthritis, asthma, psoriasis, and thrombotic disease. Leukotrienes are straight chain eicosanoids produced by the oxidation of arachidonic acid by lipoxygenases. Arachidonic acid is oxidized by 5-lipoxygenase to the hydroperoxide 5-hydroperoxyeicosatetraenoic acid (5-HPETE), that is converted to leukotriene A4, that in turn can be converted to leukotriene B.sub.4, C.sub.4, or D.sub.4. The slow-reacting substance of anaphylaxis is now known to be a mixture of leukotrienes C.sub.4, D.sub.4, and E.sub.4, all of which are potent bronchoconstrictors. There has been a research effort to develop specific receptor antagonists or inhibitors of leukotriene biosynthesis, to prevent or minimize pathogenic inflammatory responses mediated by these compounds.
Leukotrienes are released simultaneously from leukocytes with PAF, possibly from a common phospholipid precursor such as 1-O-hexadecyl-2-arachidonyl-sn-glycero-phosphocholine, and upon cellular activation, act synergistically with PAF in many biological models. European Patent Application Nos. 90117171.0 and 901170171.0 disclose indole, benzofuran, and benzothiophene lipoxygenase inhibiting compounds.
Recently, it was reported that the tetrahydrothiophene derivative of L-652,731, trans-2,5-bis-(3,4,5-trimethoxyphenyl)tetrahydrothiophene (L-653,150), is a potent PAF antagonist and a moderate inhibitor of 5-lipoxygenase. It has been disclosed that certain 2,5-diaryl tetrahydrothiophenes are PAF antagonists and leukotriene synthesis inhibitors. (Biftu, et al., Abstr. of 6.sup.th Int. Conf. on Prostaglandins and Related Compounds, Jun. 3-6, 1986, Florence, Italy; U.S. Pat. No. 4,757,084 to Biftu); WO 92/15294; WO 94/01430; WO 94/04537; and WO 94/06790.
WO 92/13848 discloses a class of racemic lipoxygenase-inhibiting hydroxamic acid and N-hydroxyurea derivatives of the structure ##STR1##
wherein R.sup.1 is hydrogen, alkyl, alkenyl, amino or substituted amino, R.sup.4 is hydrogen, a pharmaceutically acceptable cation, aroyl or alkoyl, A is alkylene or alkenylene, X is oxygen or sulfur, each Y is hydrogen, halo, cyano, hydroxy, alkyl, alkoxy, alkylthio, alkenyl, alkoxyalkyl, cycloalkyl, aryl, aryloxy, arylalkyl, arylalkenyl, arylalkoxy or substituted aryl, Z is oxygen or sulfur, m is 0 or 1, n is 1 to 5 and p is 2 to 6, inhibit the enzyme lipoxygenase.
Given the significant number of pathological immune and inflammatory responses that are mediated by PAF and leukotrienes, there remains a need to identify new compounds and compositions that exhibit PAF receptor antagonistic activity or inhibit the enzyme 5-lipoxygenase.
Therefore, it is an object of the present invention to provide compounds that reduce the chemotaxis and respiratory burst leading to the formation of damaging oxygen radicals during an inflammatory or immune response.
It is another object of the present invention to provide pharmaceutical compositions for the treatment of pathological immune or inflammatory disorders mediated by PAF or products of 5-lipoxygenase.
It is another object of the present invention to provide a method for the treatment of pathological immune or inflammatory disorders mediated by PAF or products of 5-lipoxygenase.